1. Field of the Invention
The present invention relates to a method of recycling unsaturated polyester resin waste, and more particularly, it relates to a method of recycling unsaturated polyester resin waste by chemically treating the same and obtaining industrially valuable raw material.
2. Description of the Background Art
For example, most of buttons are made of unsaturated polyester resin. Such buttons are manufactured by punching out an unsaturated polyester resin sheet and cutting out the intermediate products as obtained. In the manufacturing steps, however, about 50% of the raw material is wasted as chippings and shavings. The problem of waste disposal also arises in relation to fiber reinforced plastic products such as FRP ships and bathtubs having matrices of unsaturated polyester resin. Thus, it is desirable to recycle such unsaturated polyester resin waste.
However, it is impossible to remelt and remold waste of the unsaturated polyester resin, which is thermosetting resin having a three-dimensional network structure, dissimilarly to that of thermoplastic resin such as polypropylene, for example. Further, the unsaturated polyester resin cannot be dissolved in a solvent.
To this end, there has been made study on a method of pulverizing fiber reinforced plastic (FRP) waste having a matrix of unsaturated polyester resin and recycling the same as a filler (Yoshihiro Fukuda, Kagaku to Kogyo (Osaka), 68 (2), 60 (1994)). However, the inventors have confirmed that this method encounters such a problem that the strength of the recycled resin, which is reduced as the amount of the waste powder is increased, entirely depends on the amount of new unsaturated polyester resin.
There has been made another study on a method of degrading the aforementioned FRP under a steam atmosphere at a temperature of 500.degree. C. for obtaining components such as phthalic acid (Yoshinari Kobayashi, Kagaku to Kogyo (Osaka), 66 (10), 452 (1992); Kazuhide Hamada, Jun Hosokawa and Masashi Nishiyama, Kobunshi Ronbunshu, 49 (8), 655 (1992)). However, the high temperature of 500.degree. C. is necessary for thermally degrading the FRP, and hence this method inevitably requires a specific equipment. Further, glass fiber contained in the FRP is deteriorated due to the high temperature.